1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and more particularly to an electrophotographic photosensitive member suitable for electrophotographic printers which are provided with lasers as the light source.
2. Description of the Prior Art
Electrophotographic printers provided with lasers as the light source can reproduce images as desired, by modulating the laser beam with electric signals according to image information, scanning the surface of a photosensitive member with the modulated laser beam to form electrostatic latent images, and developing the latent images with a toner followed by transferring the toner images. Lasers generally used hitherto in these printers are gas lasers such as a helium-cadmium laser (wavelength: 441.6 nm) and a helium-neon laser (wavelength: 632.8 nm). Accordingly, photosensitive members spectral-sensitized up to about 650 nm are sufficient for these light sources. There are known photosensitive members for this purpose, for example; one having a photosensitive layer comprising a charge-transfer complex of polyvinylcarbazole with trinitrofluoreneone; one having as a photosensitive layer a vapor-deposition layer of tellurium sensitized with selenium; one having a photosensitive laminate comprising a selenium layer vapor-deposited as a charge transport layer on a conductive layer and a selenium-tellurium layer vapor-deposited on the charge transport layer; one having a photosensitive layer comprising cadmium sulfide which is spectral-sensitized with sensitizing dye; and one having a photosensitive laminate of separate function type consisting of an organic-pigment-containing charge generation layer and a charge transport layer, the sensible wavelength region of which is extended to the longer wavelength side.
Meanwhile, semiconductor lasers which are small-sized, inexpensive, and in addition directly modulable have been developed in recent years. However, most of these semiconductor lasers have a wavelength of 750 nm or more and photosensitive members as cited above are completely or virtually insensitive to rays of wavelengths of 750 nm and more. This hinders the application of semiconductor lasers to electrophotographic printers.
Lately, aluminum chloride phthalocyanine was found to be effective as a sensitive material for these semiconductor lasers, but the sensitivity thereof, when it is used in a separate function type of laminated photosensitive member, is at an insufficient level.